Lobbyist David Hallock, a former top lawyer for Gov. Mark R. Warner, has spent the last several weeks trying to come off as a highly scripted politician. Richmond attorney W. Coleman Allen Jr. has done his best as an aggressive, smooth talking trial lawyer.

Their personas: "Jerry W. Kilgore" and "Timothy M. Kaine."

On Saturday, the real Kilgore and Kaine -- Republican and Democratic nominees for governor, respectively -- will face each other in the first debate of the 2005 campaign. The 96-minute forum, a tradition that often helps define the rest of the campaign, will include questions from journalists and members of the audience and a direct exchange between the two adversaries.

To prepare, the candidates have spent hours in behind-the-scenes mock debates, using Hallock and Allen as stand-ins for their opponents in the Nov. 8 election. Aides for both camps who attended the top-secret sessions said they ranged from informal conference-table discussions to full-fledged dress rehearsals.

"We're going through the usual preparations that would be considered typical," said Tim Murtaugh, a spokesman for Kilgore, the former attorney general. "We have run-throughs. We have a briefing book that Jerry looks over. I anticipate that the other side is doing what we're doing."

Delacey Skinner, a spokeswoman for Kaine, said the "idea is to run through everything" in advance of Saturday's contest. The debate, sponsored by the Virginia Bar Association, will start at 10:30 a.m. at the Greenbrier in West Virginia. It will not be televised.

"The point of doing a mock debate is to help a candidate get comfortable with the format," she said. "The lieutenant governor is very confident in his vision and, therefore, very comfortable in this venue."

Missing from the contest will be Sen. H. Russell Potts Jr. (R-Winchester). Although he has qualified for the ballot as an independent candidate, he has not been invited to debate Kaine and Kilgore, something he has protested.

Debates have become the premier political events in Virginia campaigns, despite scant evidence that they have much of an effect on the election's outcome. As their importance has grown, so has the need for extensive "debate prep."

Kilgore aides said they have compiled a detailed briefing book, divided by topics, for their candidate to study. In their practice sessions, they said, Allen has attempted to portray Kaine as a sharp-tongued, skilled debater so that Kilgore is ready for the real thing. Senior campaign aide Chris Nolen has also taken turns playing Kaine.

"Tim Kaine is a trial lawyer, well known as a smooth talker," Murtaugh said. "People say he's Clintonian in his debating style. He's a master debater, so we're certainly taking it seriously."

Kaine's practice sessions have been equally comprehensive, according to participants.

The Democratic candidate has held several informal preparations in Northern Virginia and Richmond and has done at least two full run-throughs, complete with lecterns, colored signs to indicate how much time is left, and stand-ins for the moderator and reporters.

Hallock has provided Kaine with a debating opponent who stays on message and whose answers are polished mini-speeches, reflecting the campaign's belief that Kilgore will be well practiced when he arrives for the debate.

"He will have gone through what they foresee as every possible scenario, so he is tightly scripted," Skinner said. "We expect that they've scheduled a lot of time for debate prep. We don't underestimate Jerry Kilgore."

Strategists and advisers in both parties said preparing candidates for debates has become a virtual obsession in recent years. Campaigns devote weeks to the chore and try to steal the candidate away from precious time on the stump to make sure he's ready.

Alan Albert, a lawyer and Democratic lobbyist, has played such Republican gubernatorial candidates as Mark L. Earley and James S. Gilmore III during the last two campaigns. He also played Del. Robert F. McDonnell (R-Virginia Beach) in helping to prepare Sen. R. Creigh Deeds (D-Bath) for a debate in the attorney general's campaign.

Albert said the primary goal is a defensive one: To make sure your candidate doesn't make a gaffe that becomes a distraction for the rest of the campaign.

"When you're preparing for debates, as much as anything it's to avoid an unfortunate moment," Albert said. "Nothing different than I would do with a key witness in a case I was trying."

Aides to Kaine and Kilgore said they are videotaping the practice sessions so their candidates can see their mistakes.

"There are no handlers during that 90 minutes to run interference," said David Botkins, Earley's former communications director. "Very little can be done about a poorly delivered answer."

One thing that can be done is an immediate response from campaign staff. Each side said it will set up a war room at the Greenbrier, complete with fax machines, printers and high-speed Internet access. Press staff will rush out responses to candidate answers even before the debate is over.

One longtime Republican who has participated in coaching sessions likened the debates to NASCAR races.

"People go there looking for a wreck," said the GOP adviser, who asked not to be identified because of the ongoing campaign. "If there's not a wreck, do you remember it?"

Albert said he believes debates can be a "window" into the true personality and competency of a candidate because it's often less scripted than a speech. The goal of debate preparation is to make sure that window doesn't offer too clear a view, he said.

"It's not that you want to shut the window," Albert said. "You just don't want any frogs or bats to fly out of it."

Former state attorney general Jerry W. Kilgore is the Republican Party nominee for governor.Democratic Lt. Gov. Timothy M. Kaine will try to keep the governor's seat in his party's hands.